Synthesis of the First Stable Palladium Allenylidene Complexes

Oxidative addition of BrCCC(=O)NR2 to [Pd(PPh3)4] affords the trans-alkynylbromopalladium complexes trans-[Br(PPh3)2Pd−CCC(=O)NR2] (NR2 = NMe2 (2a), N(CH2)4) (2b)). Subsequent reaction of 2a,b with PiPr3 in excess gives trans-[Br(PiPr3)2Pd−CCC(=O)NR2] (5a,b). The analogous reaction of 2b with P(C6H4OMe-4)3 gives trans-[Br(P{C6H4OMe-4}3)2Pd−CCC(=O)NR2] (7b), and that of 2a with trifluoroacetate gives trans-[(F3CCOO)(PPh3)2Pd−CCC(=O)NMe2] (9a). Methylation of 2a,b, 7b, and 9a with either MeOTf or [Me3O]BF4 and ethylation of 2a,b with [Et3O]BF4 yield the first cationic allenylidene complexes of palladium, trans-[R*(PR′3)2Pd−CCC(OMe)NR2]+X− (R* = Br, CF3COO; R′ = Ph, C6H4OMe-4, iPr; X = OTf, BF4)

Solid-State NMR Investigations of Supported Ionic Liquid Phase Water-Gas Shift Catalysts: Ionic Liquid Film Distribution vs. Catalyst Performance

The ionic liquid film distribution in supported ionic liquid phase (SILP) catalysts has been studied by solid-state NMR. EMIMNTf2 was immobilized onto silica gel 100 support with loadings between 0 and 40?vol.-%. The 1H NMR signals indicated an exchange process between the support's surface silanol groups and the protons of the ionic liquid. At ionic liquid loadings below 10?vol.-%, islands of ionic liquids seemed to form, whereas at higher loadings complete coverage of the support was achieved. The NMR-based film model was confirmed by gas phase water-gas shift experiments using known SILP catalysts with different ionic liquid loadings. At high ionic liquid loading, the activity of the catalyst decreased due to pore blocking. The NMR technique provided easy and reliable data for film formation and distribution and allows for optimization of SILP catalysts in the future

Boosting the activity of hydrogen release from liquid organic hydrogen carrier systems by sulfur-additives to Pt on alumina catalysts

Liquid organic hydrogen carrier (LOHC) systems are a promising alternative for energy storage and transport. The development of an active and selective LOHC-dehydrogenation catalyst is therefore of great importance. In this study we present a modification procedure of Pt/Al2O3 catalysts with a sulfur containing compound that results in improved activity as well as in reduced side product formation. Here, it appears that the right amount of applied sulfur species is crucial to reach the described effects. The optimum value depends on the support surface area and the molar ratio of sulfur to surface platinum. Mechanistic studies of the sulfur modification by infrared spectroscopy (DRIFTS) with adsorbed CO revealed that preferentially low coordinated defect sites (edges or corner/apex Pt atoms) are blocked by sulfur compounds and that these are the ones responsible for side reactions. The sulfur species were found to modify the electronic properties of Pt and this facilitates the desorption of the aromatic dehydrogenation products

Influence of internal and external surface area on impregnation and activity of 3D printed catalyst carriers

Direct ink writing as additive manufacturing technique was used to print two different boehmite based shapes, cylinders and monoliths, serving as catalyst carriers. These were wet impregnated targeting 0.3–0.9 wt% platinum loadings. ICP-OES, μCT and microscopy revealed dependencies from calcination temperature, geometry and platinum loading. Dehydrogenation reactions of perhydro dibenzyltoluene as liquid organic hydrogen carrier were performed examining the catalytic performance. Differences when executing full particle measurements led to the conclusion that direct ink writing as shaping technique for catalyst carriers and the respective impregnation is highly beneficial as more complex shapes can be obtained, resulting in higher activities

Dimerization of ethene in a fluidized bed reactor using Ni-based Supported Ionic Liquid Phase (SILP) catalysts

The complexes [(mall)Ni(dppanis)][SbF6] (mall = methallyl, dppanis = (2-methoxyphenyl)diphenylphosphine) 1, [(mall)Ni(PPh3OC10)][SbF6] (PPh3OC10 = (2-decyloxyphenyl)diphenylphosphine) 2, and [(mall)Ni(PPh3OdiMePh)][SbF6] (PPh3OdiMePh = (2-(2,6-dimethylphenoxy)phenyl)diphenylphosphine) 3 were immobilized as Supported Ionic Liquid Phase (SILP) catalysts and applied for the tandem dimerization/isomerization of ethylene to 2-butene in a fluidized bed reactor. The better heat removal in the fluidized bed improves the catalyst stability and allows for a more detailed investigation of the deactivation mechanism. Based on kinetic studies, a second order deactivation mechanism is proposed, in which two nickel complexes dimerize if the supply of ethene is insufficient

Allenylidene Complexes with Extended π-Sytems: Synthesis, Spectroscopy and Electron-Transfer Properties

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